A mechanical property of a given volume of a material can vary depending on the direction of the measurement of such property. Variations in such a mechanical property with azimuth can lead to differences in the patterns of fluid flow through the material and can control the direction of propagation of natural and induced fractures in the material. This variation of mechanical property with azimuthal direction is termed "anisotropy". Such mechanical anisotropy can be caused by near parallel fractures, in-situ stress, depositional patterns, or crystal alignment within the material. Knowledge of mechanical anisotropy is important in identifying stress cracking in brittle materials, fluid flow patterns in porous material and fatigue cracking in metals or ceramics. For example, the anisotropy of elastic properties or anisotropy caused by fractures may affect the interpretation of seismic prospecting data. In petroleum production, permeability anisotropy, caused by preferential arrangement of pores and/or fractures, is often an important factor in both primary and secondary enhanced recovery. Stress anisotropy is important in petroleum well stimulation by hydraulic fracturing because the azimuth of induced fractures is generally parallel to the maximum horizontal stress direction. In many cases, the directions of natural and induced fractures are coincident.